@FranklinRobson There's an elixir (Supernatural expansion) called "Lean and Mean" that causes a sim to lose weight. A sim needs to be at least at level four of the Alchemy skill to brew it, but you might find it at the elixir shop.
The Body Sculptor lifetime reward (30k points) allows you to choose the weight of your sim.
I've read that body sculptor too has an effect that dissipates. And for Lean and Mean they will regain their muscle mass and weight too sadly. The difference being is that you don't need to seek out ingredients to use body sculptor.
@FranklinRobson I think the Plastic Surgery option at the hospital (requires the Pets EP) might work, but I've never tried it. If that and the Body Sculptor LTR (which I've never tried either) don't change a sim's genetic weight, you might need to use a mod or cheat.
@FranklinRobson I remember the body sculptor effect being just temporary. I think I often succeeded changing looks with the plastic surgery. It has its own in-built randomness in gameplay as well though, so be prepared.
